The sialic acid-like sugar 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto-nonulosonic acid, or legionaminic acid, is found as a virulence-associated cell-surface glycoconjugate in the Gram-negative bacteria Legionella pneumophila and Campylobacter coli. L. pneumophila serogroup 1 strains, causative agents of Legionnaire's disease, contain an α2,4-linked homopolymer of legionaminic acid within their lipopolysaccharide O-chains, whereas the gastrointestinal pathogen C. coli modifies its flagellin with this monosaccharide via O-linkage. In this work, we have purified and biochemically characterized eleven candidate biosynthetic enzymes from C. jejuni, thereby fully reconstituting the biosynthesis of legionaminic acid and its CMP-activated form, starting from fructose-6-P. This pathway involves unique GDP-linked intermediates, likely providing a cellular mechanism for differentiating between this and similar UDP-linked pathways, such as UDP-2,4-diacetamido-bacillosamine biosynthesis involved in N-linked protein glycosylation. Importantly, these findings provide a facile method for efficient large-scale synthesis of legionaminic acid, and since legionaminic acid and sialic acid share the same D-glycero-D-galacto absolute configuration, this sugar may now be evaluated for its potential as a sialic acid mimic.

Campylobacter jejuni, sialic acid, legionaminic acid, flagellin glycosylation, neuraminic aid

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
5,0,0,2	Ac
5,0,0,4	Ac
5,0,0	aDQuipN4N	95.4	55.2	69.8	57.9	69.3	18.0
5,0	P
5	P
	xXnucG


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
5,0,0,2	Ac
5,0,0,4	Ac
5,0,0	aDQuipN4N	5.50	4.05	3.80	3.68	4.05	1.16
5,0	P
5	P
	xXnucG


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
5,0,0,2	Ac
5,0,0,4	Ac
5,0,0	aDQuipN4N	95.4/5.50	55.2/4.05	69.8/3.80	57.9/3.68	69.3/4.05	18.0/1.16
5,0	P
5	P
	xXnucG

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@H]1[C@H](O)[C@@H](NC(C)=O)[C@@H](OP(=O)(O)OP(=O)(O)OC[C@H]2O[C@@H](n3cnc4c(=O)[nH]c(N)nc43)[C@H](O)[C@@H]2O)O[C@@H]1C

671.45 g/mol (C₂₀H₃₁N₇O₁₅P₂)